Silicone hydrogel (SiHy) contact lenses are widely used for correcting many different types of vision deficiencies. They are made of a hydrated, crosslinked polymeric material that contains silicone and a certain amount of water within the lens polymer matrix at equilibrium.
Water in a SiHy contact lens can provide the desirable softness that enable a SiHy lens to be worn for sufficiently long periods of time and provides patients with the benefits including adequate initial comfort (i.e., immediately after lens insertion), relatively short period of adapting time required for a patient to become accustomed to them, and/or proper fit. Higher water content would be desirable for providing SiHy contact lenses with biocompatibility and comfort. But, there is a limit to the amount of water (believed to be 80%) that a SiHy contact lens can contain while still possessing sufficient mechanical strength and rigidity required for a contact lens, like conventional hydrogel contact lenses. Moreover, high water content could also have undesired consequences. For instance, oxygen permeability of a SiHy contact lens could be compromised by increasing water content. Further, high water content in a SiHy lens could result in greater in-eye dehydration and consequently dehydration-induced wearing discomfort, because a SiHy contact lens with a high water content could deplete the limited supply of tears (water) of the eye. It is believed that in-eye dehydration may be derived from evaporation (i.e., water loss) at the anterior surface of the contact lens and such water loss is primarily controlled by water diffusion through a lens from the posterior surface to the anterior surface, and that the rate of diffusion is closely proportional to the water content of the lens bulk material at equilibrium (L. Jones et al., Contact Lens & Anterior Eye 25 (2002) 147-156, herein incorporated by reference in its entirety).
Incorporation of silicone in a contact lens material also has undesirable effects on the biocompatibility of the contact lens, because silicone is hydrophobic and has great tendency to migrate onto the lens surface being exposed to air. As a result, a SiHy contact lens will generally require a surface modification process to eliminate or minimize the exposure of silicone of the contact lens and to maintain a hydrophilic surface, including, for example, various plasma treatments (e.g., Focus® Night & Day® and Air Optix® from Alcon; PureVision® from Bausch & Lomb; and PremiO™ from Menicon); internal wetting agents physically and/or chemically embedded in the SiHy polymer matrix (e.g., Acuvue® Oasys®, Acuvue® Advance® and Acuvue® TruEye™ from Johnson & Johnson; Biofinity® and Avaira™ from CooperVision). Although surface modification techniques used in the commercial SiHy lens production may provide fresh (unused) SiHy lenses with adequately hydrophilic surfaces, a SiHy lenses worn in the eye may have dry spots and/or hydrophobic surface areas created due to air exposure, shearing forces of the eyelids, silicone migration, and/or partial failure to prevent silicone from exposure. Those dry spots and/or hydrophobic surface areas are non-wettable and susceptible to adsorbing lipids or proteins from the ocular environment and may adhere to the eye, causing patient discomfort.
Therefore, there is still a need for cost-effective methods not only for improving the wettability of silicone hydrogel contact lenses but also for rendering such a wettability sustainable.
The following publications: U.S. Pat. Nos. 6,099,122, 6,367,929, 6,436,481, 6,440,571, 6,447,920, 6,451,871, 6,465,056, 6,500,481, 6,521,352, 6,586,038, 6,623,747, 6,630,243, 6,719,929, 6,730,366, 6,734,321, 6,793,973, 6,822,016, 6,835,410, 6,878,399, 6,884,457, 6,896,926, 6,923,978, 6,926,965, 6,940,580, 7,052,131, 7,249,848, 7,297,725, and 8,529,057; and U.S. Pat. Appl. Pub. Nos. US 2007/0229758A1, US 2008/0174035A1, and US 2008/0152800A1), US 2008/0226922 A1 and 2009/0186229 A1, US 2008/0142038A1, US 2009/0145086 A1, 2009/0145091A1, 2008/0142038A1, and 2007/0122540A1, disclose various surface modification methods for rendering silicone hydrogel contact lenses wettable.
The following publications: U.S. Pat. Nos. 5,882,687, 5,942,558, 6,348,507, 6,440,366, 6,531,432, 6,699,435, 8,647,658, and 8,689,971; and Published PCT Patent Applications WO9720019 and WO2006/088758, disclose that surfactants or lubricants are added in the lens packaging solution to ease to some extent initial discomfort and other symptoms.